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CU-Boulder study: Grand Canyon about 65 million years older than thought

New research indicates canyon was formed 70 million years ago

By Charlie Brennan Camera Staff Writer

Posted:
11/29/2012 12:00:00 PM MST

A new study co-authored by Rebecca Flowers, an assistant professor in geological sciences at the University of Colorado, indicates the Grand Canyon was largely carved by about 70 million years ago, some 65 million years earlier than the conventionally accepted date. (Photo courtesy PDPhoto.org )

The latest best estimate on the age of the Grand Canyon is taking more than a canyon-sized leap back in time -- almost 65 million years, in fact.

Rebecca Flowers, an assistant professor in geological sciences at the University of Colorado, is co-author of a paper published online today in Science magazine, which puts the age of the Grand Canyon's formation at 70 million years. At that time, dinosaurs still walked the earth.

Previously, the most widely accepted estimates put the Grand Canyon's age at a relatively sprightly 5 million to 6 million years, based on the age of gravel washed downstream by the ancestral Colorado River. Also, a previous Science magazine report in 2008 set it at 17 million years old.

The new study by Flowers, co-authored by professor Kenneth Farley at the California Institute of Technology, bases its findings on analysis of mineral grains at the bottom of the western Grand Canyon.

"This is going to be controversial," Flowers said. "The age of the Grand Canyon has been controversial for more than 150 years, and I think it's going to continue to be. There are people who very firmly believe in a young age, even though the evidence doesn't require that it be young.

"This ancient canyon idea can be tested with additional data, and I am hopeful that is what's going to happen. I'm certain that is going to happen."

At the canyon itself, officials were unmoved today. They were not scurrying for 65 million additional birthday candles for the next cake.

"Without our scientists having a chance to review the study, we would not provide comment on it," said Maureen Oltrogge, a U.S. National Park Service public affairs officer at Grand Canyon National Park.

The Grand Canyon, located in northern Arizona, is more than a mile deep in some spots, about 280 miles long and up to 18 miles across. It draws more than 5 million visitors each year who come away awestruck at a colorful vista that can appear transformed almost minute to minute as the sun crosses the sky.

Geologists long have agreed that there is some rock in the bowels of the gorge that is 2 billion years old. Flowers acknowledges that, and the study doesn't contest that. Rather, it addresses the formation of the entire present-day canyon, not simply the age of any one rock that might be found there.

'Big implications'

Flowers and Farley based their dating on methods that utilize the radioactive decay of uranium and thorium atoms to helium atoms in a phosphate mineral known as apatite.

Thelium atoms were locked in the mineral grains as they cooled, and moved closer to the surface during the carving of the Grand Canyon, Flowers said. Temperature variations at shallow levels beneath the earth's surface are affected by topography, and the thermal history recorded by the apatite grains enabled researchers to infer how much time had passed since there was significant natural excavation of the canyon, according to Flowers.

"It does have some big implications for western United States evolution, whether or not you believe in a young canyon or an old canyon," Flowers said. "We know that 70 million years ago, there were highlands to the west and lowlands to the east. This would indicate that the river that carved the Grand Canyon flowed from west to east -- which is different from today's movement."

As areas to the east of the present-day Grand Canyon rose in topography, the areas to the west "collapsed," Flowers said, leading to the reversal of the river's flow.

Placing this dramatic change to the landscape 65 million years further back in time, Flowers said, "has some larger implications for how you think that western United States topography, drainage systems and landscapes evolved over the last 70 million years."

In an earlier 2008 study, Flowers and colleagues showed parts of the easternmost section of the canyon -- that which is seen by most visitors from the North and South rims -- likely developed about 55 million years ago, although the bottom of the ancient canyon then was actually higher than the current canyon rim, before eroding to its current depth.

Now, she said, "There is a range of dates that is permissible, and the data are consistent with carving of that eastern part by 70 million years, as well."

'Long and complicated history'

Recently, U.S. Sen. Marco Rubio, R-Fla., created headlines in responding to a GQ magazine interviewer, saying he believed the age of the earth to be "a dispute among theologians."

Flowers prefers to frame the discussion in terms of what can be put to the scientific test through geochronology.

"The earth is 4.6 billion years old, and has a long and complicated history," she said. "I've never been exposed to any of that (alternative, non-scientific interpretations of the earth's formation), but I would be interested to see if I am contacted by people."

Flowers has visited the canyon a half-dozen times herself. An ultra-distance runner, she also has run to its bottom -- and back.

Her future plans for the Grand Canyon are still in formation.

"I'm interested in seeing the reaction of this (scientific) community to this project," she said. "I do want to continue working there. I don't have very specific plans for what that will entail, but I plan to continue working on these general problems in the future."

Patrick O'Driscoll, a National Park Service public affairs officer for the Intermountain Region based in Denver, said, "Whatever age the Grand Canyon itself is, the dozen or so different rock layers through which the Colorado River carved the canyon date back nearly 2 billion years.

"Learning to tell them apart from each other is one of those rare treats when you hike into the canyon or float down the river."

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